The preferred embodiment concerns a method and an arrangement to generate a predetermined revolution speed of a continuous, belt-shaped image substrate (support), as well as a method to determine the curve of the revolution speed of a continuous, belt-shaped image substrate (support). At least two color separations are generated on the image substrate and transferred from the image substrate onto a substrate material to generate a print image. An offset is also determined between the at least two color separations of the print image, which is also designated as a registration error. A registration error exists when at least two color separations are not printed exactly atop one another and thus are not precisely in register. A fuzzy appearance of the print image is thereby generated. In printing technology, the exact superimposed printing of multiple color layers (i.e. multiple color separations) in multicolor printing is designated as a registration.
It is known to print what are known as registration characters or registration marks next to or in the print image, via which the registration errors can be visually depicted. In electrographic (especially electrophotographic) printers or copiers, the individual color separations are generated in succession on the same photoconductor, or each on its own photoconductor, and are collected on an intermediate image substrate. A first color separation as a toner image is thereby generated on a photoconductor and transfer-printed onto the intermediate image substrate in a first transfer printing revolution thereof. A second color separation generated with the aid of the photoconductor is subsequently transfer-printed (with optimally precise registration relative to the first color separation) onto the intermediate image substrate during a second revolution of the intermediate image substrate, and thus the first color separation is overlapped with precise registration.
An additional revolution of the intermediate image substrate is respectively provided for possible additional color separations. The generation of the individual color separations and the transfer printing of these color separations during multiple revolutions of the intermediate image substrate is also known as a collection or as a multicolor printing collection mode of the printer or copier. The transfer printing of the color separations collected on the intermediate image substrate onto a substrate material to be printed is only activated after all required color separations are at least partially present on the intermediate image substrate. For example, such an activation of the transfer printing station occurs by moving the intermediate image substrate onto the substrate material and/or by moving the substrate material onto the intermediate image substrate.
If a print image with two color separations should be generated, during the generation of the first color separation and at least one part of the second color separation the intermediate image substrate is arranged at a distance from the substrate material and thus has no contact with the substrate material. By moving the intermediate image substrate and/or the substrate material forward and back, a web-shaped substrate material (for example a paper web) can also be printed in multiple colors, i.e. with a print image with multiple color separations of different colors. For example, a printer for multicolor printing of a paper web is known from the published patent application WO 98/39691 and the parallel U.S. Pat. No. 6,246,856 B1. In this known printer the intermediate image substrate is executed as a transfer belt. Also known from these publications are printers with oppositely arranged printing groups by which a paper web can be simultaneously printed in one and/or multiple colors on the front side and the back side.
In addition to the aforementioned multicolor printing collection mode, these known printers can be operated in a continuous printing mode. Only one color is printed in continuous print mode. Only one color separation of a primary color is generated in single color printing. Thus no color separations are collected on the transfer belt in continuous printing mode. Instead of this, the toner image is transfer-printed from the photoconductor onto the transfer belt and directly printed onto the paper web at the transfer printing point in the course of a continuous processing.
The colors of the individual color separations (both in multicolor printing collection mode and in continuous printing mode) can be generally typical primary colors—such as cyan (C), magenta (M), yellow (Y), black (K)—or a special color of a desired color value. Such special colors are in particular offered by the applicant under the designation Océ Custom Tone. Additional information regarding the Océ Custom Tone colors is described in Chapter 3 in the document “Digital Printing—Technology and Printing techniques of Océ Digital Printing Presses”, February 2005, 9th Edition, ISBN 3-00-001081-5. The statements contained in this document regarding color printing (in particular with regard to multicolor printing) are herewith incorporated by reference into the present specification. The design and the embodiment possibilities of electrographic printers for single and multicolor printing of a web-shaped substrate material that are known in the documents WO 98/39691 and U.S. Pat. No. 6,246,856 B1 are likewise herewith incorporated by reference into the present specification.
In known printers or copiers, the revolution speed of the intermediate image substrate is slightly greater than the transport speed of the substrate material so that the intermediate image substrate is braked after it is in contact with the substrate material due to moving the intermediate image substrate onto the substrate material and/or due to moving the substrate material onto the intermediate image substrate. The slippage between the intermediate image substrate and a drive roller to drive the intermediate image substrate is thereby increased. The revolution speed of the intermediate image substrate thus changes via the pivoting of the intermediate image substrate onto the substrate material and/or via the pivoting of the substrate material onto the intermediate image substrate, as well as due to pivoting the intermediate image substrate away from the substrate material and/or due to pivoting of the substrate material away from the intermediate image substrate.
To drive the intermediate image substrate, the drive roller has a constant drive speed to generate a constant revolution speed. Due to the change of the revolution speed as a result of contacting the intermediate image substrate with the paper web, the revolution speed of the intermediate image substrate changes (possibly repeatedly) during the image generation process. These changes lead to fluctuations in the curve of the revolution speed of the intermediate image substrate and to different registration errors in the longitudinal direction (i.e. in the transport direction) of the substrate material. The effects that lead to such fluctuations of the revolution speed of the intermediate image substrate are, however, known only in part and interfere with one another. Given known speed changes, for example upon pivoting the intermediate image substrate onto the substrate material, registration errors can be changed due to a corresponding change of the drive speed of the intermediate image substrate, as this is known from the document DE 103 38 497 B4, for example. The content, in particular the procedure to avoid registration errors, is herewith incorporated by reference into the present specification.